Shoulder Screws Information

Various Sizes of Precision Shoulder Screws image








Shoulder screws are a type of machine screw with integral threads that are only present on half or less of the screw shank. A shoulder screw has a partially smooth shaft that will allow the bolted material some rotation and movement around the screw axis, while the threaded end will typically have a nut to maintain the screw's position. These screws must be used with predrilled holes, and are common in machinery with vibration and heat variations. These are also called stripper bolts.


Shoulder Screw Operation


Like other screws, shoulder screws are meant to hold objects together and in position. However, they do not have a tapered shank, so they do not self-thread into soft materials. They are used in instances where pre-tapped holes require alignment with some tolerance. This allows the workpieces either a joint, pivot, or sliding motion. These screws are available in metric and imperial units.


Shoulder screws have three sections: head, shoulder, and thread. The head is the largest diameter section of the shoulder screw, which prevents the screw from being inserted further than its length, and provides a bearing surface, as well as a drive mechanism (slotted, hex, etc.) so the screw can have torque applied for its installation. The shoulder is the smooth, middle section of the screw which contains the lateral movement of the workpieces. The threaded section has helixed grooves that have a major diameter slightly smaller than the shoulder diameter. This section is for insertion into a mating thread, be it a nut or tapped hole.


Shoulder Screw diagram



Shoulder Screw Production


Bolts and screws are created by the same manufacturing process: cold forging. Minor variances in production result in the capped head and ground shoulder that is prevalent on shoulder screws.



Video credit: Discovery Channel via Youtube / CC BY-SA 4.0


Screw Drive Options


Shoulder screws are produced with several types of screw head drive. This enables torque to be applied to the machine screw to be rotated around its thread and into a tapped hole.


Shoulder Screw Screw Head Drives dia gram


Tamper resistant designs exist to prevent, or at least deter, unauthorized screw removal. They include:


Shoulder Screw Tamper-resistant Drives diagram


Screw Materials


Shoulder screws are almost always made out of a type of steel.


  • Hardened steel relies on hardening methods to produce a stronger, but more brittle, version of steel.
  • Unhardened steel screws are produced of strong, carbonated iron. Uncoated steel is vulnerable to corrosion.
  • Stainless steel screws are chemical and corrosion resistant with an appealing finish. They cannot be hardened like carbon steel.
  • Brass has natural lubricity so it works well with moving components under light loads

  • Plastic screws are inexpensive and corrosion resistant for very light loads.

Screw Finishes


Finishes applied to the base metal of the screw enhance the durability and corrosion resistance of the material.


  • Black oxide finishes do not enlarge the dimensions of the screw and is a processed black rust. It is mostly used for aesthetic purposes.
  • Chrome coating is a bright, reflective finish that is decorative and very durable. It is applied via electropating.
  • Zinc plated coatings act as a sacrificial anode, protecting the underlying metal. It is applied as a fine white dust.

  • Other coatings like galvanization and phosphating are common for particular types of hardware, like screws meant for fence or window applications.

Screw Dimensions


Shoulder screws have different dimensional specifications than other machine or cap screws due to their ground, smooth section.


Shoulder Screw dimensions

Image credit: Machine Design



Since shoulder screws can be used as a type of bearing or linear slide, some tolerance is usually granted to the shoulder diameter. Precisions-grade shoulder screws will have tolerances from .0005  to .0015 inches (.013 and .038 mm) below their nominal size.


Commercial grade screws have varying screw tolerances. For all imperial unit screws, tolerance range is .002 and .004 inches below the labeled size. Metric tolerances change according to the predetermined diameter.


Nominal shoulder diameter (mm)

Tolerance below labeled diameter (mm)

6.5 — 10

.013 — .036

13 — 16

.016 — .043

20 — 25

.020 — .052


Thread Standards


Hardware fasteners, like screws, are generally formulated to meet the standards of either ISO, DIN, or ASME/ANSI. For shoulder screws, the most critical interpretation of screw standards is the thread pitch. 


Metric Units

ISO and DIN standards are based upon the metric system and are closely related (ISO guideline 261). Most hardware measured in imperial units is subject to Society of Automotive Engineers (SAE) edict as well. These standards are common in the majority of the world, and speculation exists that this may become a global hardware standard. The threads on shoulder screws can be available in both fine and course pitch configurations

Shoulder screw thread pitch


Imperial Units

ASME/ANSI standards are based upon the imperial inch, and are most common in the North American marketplace. These standards assess an 18-digit PIN number to unique hardware pieces to substitute cumbersome design descriptions. Pitch in imperial units is represent by teeth-per-inch (TPI), which also comes in fine and coarse varieties.

Shoulder screw imperial ASME ANSI sizes TPI fine coarse table chart




Shoulder screws are common on the core engine block in autos. They are suitable for joints that are burdened with a heavy shear load. They are useful in conjunction with springs; they are frequently used on vehicle leaf springs, or as an internal, threadless guide for compression springs. The wheels on some sliding drawers are mounted with shoulder screws, so stripper bolts are sometimes used as simple axles.

Shoulder screw Alfa Romeo engineSelect stripper bolt shoulder screw for die stamp spring guide internalLeaf spring with shoulder screw and stripper bolts

Image credit: International Auto; Fastenal; RC4WD




Machine Design - The Basics of Shoulder Screws - What are Shoulder Screws?


Shopwiki - Shoulder Screws


Bolt Depot - Shoulder Bolts


Wikipedia - Screw - Screw


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